1. Field of the Invention
The invention relates to dry powder skin care compositions useful as baby powders, body talcs, deodorizing powders, OTC eczema preparations, foot powders, anti-fungal powders, etc. More particularly, the invention relates to stable dry powders having prolonged and controlled release properties. The dry powder is preferably prepared by a process comprising spray-drying a mixture of liposome encapsulated active agent, modified starch and maltodextrin. The particle is designed so that activity of, e.g., an anti-inflammatory agent such as Dragosantol.RTM. can be specifically triggered by skin conditions, such as moisture, for optimal effect.
2. Description of the Related Art
Prevention of diaper dermatitis, i.e., diaper rash, involves keeping a baby's delicate skin dry and free of irritants. Topical powders having drying properties, referred to herein as dry powders, are commonly applied to assist in physically absorbing moisture and preserving skin dryness. Drying powders are typically either corn starch based or talcum based. However, corn starch may be irritating to sore skin, and baby talcum powder can be harmful to an infant's lungs if inhaled during diaper changing.
In comparison to the above-described physically acting topical composition, another type of skin care product is based upon a pharmaceutical agent which must usually be delivered via a specially formulated topical composition. For example, bisabolol is a biologically active agent known to have antiphlogistics and antibacterial properties. When used in a product in a standard formulation, the whole amount of bisabolol is released at the time of application; so there is an initial burst of activity which phases out quickly. In order to delay and prolong the release of such fast acting pharmaceutical agents, it is known to incorporate these active substances in microcapsules or matrices.
However, neither of these approaches alone is satisfactory in conditioning the skin. Even when both approaches are used in combination they may not provide the greatest amount of active agent at the precise time of greatest need. Consumers are becoming increasingly educated and expect a high level of sophistication in their products. There is thus a need for an intelligent skin care product which can provide not only physical absorbency of moisture and prolonged release of active agent, but which also coordinates peak delivery of active agent to a particular biological demand, such as skin wetness. This responsive delivery is referred to herein as controlled delivery. A baby powder product recently marketed by CreativeCare BabY Line [sic] uses ultra refined oat particles medicated with zinc oxide, a mild neutralizer and astringent, as "micro-sponges" with natural anti-itch and anti-irritant properties. However, there is room for improvement in the feel and controlled efficacy of the product.
In recent years increasing attention has been paid to the development of liposomes for use as "containers " for substances which are intended to be liberated upon reaching a target site. Liposomes are small, closed vesicles formed from lipids, usually phospholipids. Lipids generally have a hydrophobic "tail" and a hydrophilic "end". When mixed with water, hydrophobic ends tend to join toward a common center while the hydrophobic tails become oriented outwardly to interface with the water. The lipids may form a monomolecular layer or may arrange themselves in more than one layer of lipids, to form a "liposome" having an inner space and an outer surface. Liposomes may also have more than one layer.
Liposomes have been used to deliver active agent to the skin. For example, U.S. Pat. No. 5,128,139 (Brown et al.) teaches a deodorant comprising liposomes containing grapefruit seed extract. The bioactive agents are entrapped within multilamellar liposomes complexes to provide release over time. Brown et al. acknowledge that liposomes are inherently unstable and tend to break apart, releasing the contents within. Brown et al. thus layers the liposomes or forms them into clusters such that the liposomes which are confined within or are sandwiched between outer layers of liposomes are protected and are more likely to remain stable. The outer liposomes tend to break apart releasing their contents while protecting the inner liposomes for later degradation and release. While the product provides for prolonged release of active agent, there is no discussion of controlled release, i.e., timing release so as to peak when needed.
U.S. Pat. No. 4,937,078 to Mezie et. al. discloses the incorporation of topical anesthetic actives into liposomes which essentially encapsulate the active ingredient within layers of lipid material. It is reported that the lipid vesicles provide a more pronounced cutaneous anesthetic or analgesic effect while employing less of the topical anesthetic agent. The lipid vesicles allegedly provide a means of prolonging the permeation rate without the risk for discomfort due to numbness or systemic reactions. However, prolonging release simply refers to constant rate of release over an extended period of time. There is no mention of masking active agent until need, then releasing an amount of active agent commensurate with the need.
U.S. Pat. No. 5,510,120 (Jones, et al.) teaches a cosmetic composition for topical application to the skin and/or hair. The composition comprises particles (microcapsules or liposomes) which enclose a cosmetically-effective benefit agent (e.g., an agent intended to modify or enhance body odor) active at a target location accessible by application to the skin and/or hair. The particles have means, namely lectin, for binding to targeted microorganisms present on the skin and/or hair, for example those bacteria responsible for skin disorders, scalp irritation, and underarm and foot odor. The encapsulated active agent may be "combined" with a vehicle or carrier such as water, various liquid substances, and various powders such as chalk, talc, fullers earth, kaolin, starch, gums, colloidal silica, sodium polyacrylate, tetra alkyl and/or trialkyl aryl ammonium smectites, chemically modified magnesium aluminum silicate, organically modified montmorillonite clay, hydrated aluminum silicate, fumed silica, carboxyvinyl polymer, sodium carboxymethyl cellulose, ethylene glycol monostearate.
While Jones et al. teach targeting delivery of active agent in terms of location, they do little to target delivery in terms of time, i.e., controlling release to peak at the time of greatest need.
U.S. Pat. No. 4,508,703 (Redziniak et al.) teaches a method of preparing a pulverulent mixture of amphiphilic lipidic constituents (e.g., phospholipids) by adding fine solid microalveolate particles (such as kieselguhr) and atomization (col. 6, lines 40-45). The particles are then rehydrated to produce hydrated lipidic lamellar phases. There is, however, no mention of applying a powder to skin.
Accordingly, there remains a need for a new type of delivery system which satisfies a number of requirements, namely, it must be capable of formulating even labile compounds, it must provide enhanced stability, it must be aesthetically pleasing, it must increase efficacy, and it must have reduced irritancy, it must remain in place, and most importantly, it must remain capable of releasing active ingredient in response to biological demand.